1. Field of the Invention
This invention relates to articles having an elastomer fixed to a substrate of a rigid material such as a metal, and more particularly to orthopedic devices having elastomeric members bonded to rigid members, such as prostheses for replacing a mammalian intervertebral spinal disc, implants for artificial joints, prosthetic ligaments and tendons, and the like, wherein an elastomeric member is firmly bonded to a rigid endplate or other structure for attachment to bone.
2. Background Art
Low back pain is a very common pathological condition, affecting approximately 80% of the general population at some time. Although most patients experience the painful symptoms only occasionally and recover fully, approximately 10% of these patients come to experience chronic and disabling low back pain in spite of various medical treatments.
The most common cause of chronic disabling low back pain is degeneration of one or more of the intervertebral discs that are positioned between the vertebrae of the spine and permit the various natural movements of the spinal column. Such degenerative disc disease (DDD) may become intractable to non-surgical treatment and have to be treated by surgical intervention. Spinal fusion has been a traditional and generally effective treatment method for chronic disabling low back pain that is not responding to non-operative treatments. More recently, alternative treatments involving replacement of the entire disc or its nucleus have been developed for treatment of discogenic pain.
The first generation of prostheses for replacement of degenerated intervertebral discs has generally incorporated mutually sliding surfaces of relatively hard materials to provide for the required intervertebral motion in flexion, extension, lateral bending and torsion. Although such prostheses have been found to be helpful, improvements in shock absorption and replication of the natural motion of the intact intervertebral disc have been sought.
Accordingly, subsequently developed prostheses have incorporated elastomeric members in order to provide for the required motion and shock absorption. Such prostheses typically include relatively hard endplates for contacting the endplates of adjacent vertebrae and fixing the prosthesis thereto, together with an elastomeric disc core, positioned between the hard endplates and attached thereto.
Attachment of the elastomeric core of such prostheses to their hard endplates has hitherto been accomplished generally by adhesives, by mechanical interlocking undercuts or the like, or by providing a porous surface on the hard endplate which engages the elastomeric core, or combinations of such techniques. For example, it has been proposed to cover the surface of the endplate that contacts the elastomeric core with a coating of small generally spherical beads bonded to that surface, e.g., by sintering or the like. The elastomeric core may then be molded against the bead-covered surface, or otherwise applied thereto, whereby the elastomer infiltrates the porous bead coating and provides a substantial mechanical interlock between the hard endplate and the elastomeric core. Such bonding surfaces are disclosed, e.g., in U.S. Pat. No. 5,071,437.
Nevertheless, a need has continued to exist for alternative methods of securing hard elements of orthopedic devices, such as an endplate of an intervertebral disc prosthesis, to elastomeric elements such as the elastomeric core of an intervertebral disc prosthesis.